Duchess of Cambridge, 35, is expecting her third child in April 2018.

Catherine, Duchess of Cambridge, talks to children and tennis player Johanna Konta as she visits the Lawn Tennis Association at National Tennis CentreGetty

Pregnant Kate Middleton cut an uncharacteristically casual figure on her royal engagement to the National Tennis Centre to learn more about their work today (31 October).

The Duchess of Cambridge – who is expecting her third child with husband Prince William in April 2018 – looked like she meant business and ready to play a spot of tennis as the new patron of the Lawn Tennis Association (LTA).

Kate, 35, still managed to look glamorous in a pair of flattering black and white trousers worth £220 paired with a matching fleece by Monreal London and white Nike trainers which retail at £170, tying her brunette locks back into a neat ponytail.

Tennis fanatic Kate, who has been brought up watching and playing the sport, was in her element while meeting and competing against the zealous young tennis players at the event.

She was seen taking advice from tennis player Johanna Konta with the children before throwing herself into the activities and proving that her pregnancy is not getting in her way of her energy.

The royal appears to have gotten over the worst of her acute morning sickness – otherwise known as hyperemesis gravidarum – resuming royal duties earlier this month by attending three engagements with Prince William and Harry.

Kate visits the Lawn Tennis Association at National Tennis CentreGetty

Today marks her first solo outing since announcing her third pregnancy, and she is set to have a more relaxed afternoon watching some on-court sessions including a Tennis for Kids Event, along with meeting some of the UK's top junior talents.

She will also spend time with youngsters who are participating in the Coach Core apprenticeship scheme.

Kate enjoying some tennis activities with a little girl at the National Tennis CentreGetty

The duchess became patron of the LTA last December, taking over from the Queen who previously held the role for 64 years. She couldn't be a better member of the royal family to take on the position, previously claiming that the sport was part of her childhood.

Kate said: "It is such a quintessential part of English summer. I was really taken by Agassi and Sampras, Ivanisevic and Steffi Graf. That for me was my first memories."

Kensington Palace announced earlier this month that Kate – who is in her second trimester – is due to welcome the latest addition to her and William's family in April. She will be heavily pregnant on an official visit to Norway and Sweden with the duke early next year.